1. Field of the Invention
The present invention is directed to computer systems. More particularly, it is directed to sharpening of graphic images.
2. Description of the Related Art
People frequently over sharpen areas of an image because some images, or regions of images, may include areas that are sharp and areas that are not sharp. In an effort to sharpen the areas that are blurry, a user may inadvertently over sharpen areas that are already sharp. For example, a graphics tool may only be configured to sharpen every pixel in selected region. Additionally, traditional graphics programs frequently are configured only to sharpen the image as a whole. Moreover, while some graphics tools may allow a user to select a specific region for sharpening, it may be very difficult and tedious for the average user to manually select different regions for sharpening while avoiding those areas that are already sharp.
Some image tools may include an edge-sharpening algorithm that automatically attempts to locate and sharpen the edges of objects in an image. However, traditional edge-sharpening are not selective in the areas of the image to which edge-sharpening may be applied. In other words, if the image tool locates what it believes is an edge, it will sharpen it, typically without allowing any user control. Other traditional imaging sharpening techniques, such as Unsharp Mark (USM) may allow a user to specify a sharpening threshold to be applied to an entire image, thus often resulting in over-sharpening already sharp areas of the image.
FIGS. 1A, 1B, 1C and 1D illustrate sharpening of an image. Please note that FIGS. 1A, 1B, 1C and 1D are not meant to illustrate any particular method of sharpening, but instead are intended to illustrate general sharpening of an image. FIG. 1A illustrates an image that includes two overlapping ellipses with blurry edges as can be seen in FIG. 1C, which illustrates a magnified view of the section of FIG. 1A within the dashed rectangle. FIG. 1B illustrates the same section of FIG. 1A after applying sharpening. As is apparent from FIG. 1C, in which each rectangle of color may be considered a single pixel, the contrast in color between some pairs of adjacent pixels is higher than the contrast between other pairs of adjacent pixels. When sharpening is applied to the areas of the image in FIG. 1A that include higher contrast between adjacent pixels, the pixel values may be adjusted so as to provide even more contrast between adjacent or nearby pixels, as illustrated in FIG. 1D. Over sharpening an image may result in a ‘halo’ effect, as is illustrated in FIG. 1B.